Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $24.86   7.132%   $26.633   $26.63   $26.65   $26.60  
  Purchase #2 $246.60   9.226%   $269.3513   $269.35   $269.35   $269.40  
  Purchase #3 $190.69   9.486%   $208.7789   $208.78   $208.80   $208.80  
  Purchase #4 $18.37   8.351%   $19.9041   $19.90   $19.90   $19.90  
  Purchase #5 $118.62   6.328%   $126.1263   $126.13   $126.15   $126.10  
  Purchase #6 $98.79   5.139%   $103.8668   $103.87   $103.85   $103.90  
  Purchase #7 $155.52   11.831%   $173.9196   $173.92   $173.90   $173.90  
  7 purchase totals = $853.45       $928.5800   $928.58   $928.60   $928.60